Seismic exploration



1965 H. c. JOHNSEN 3,212,599

SEISMIC EXPLORATION Filed Nov. 8, 1961 4 Sheets-Sheet 1 COMMON SECTIONCABL E TAKEOUT FIG. 2

INVENTOR. ip H.C. JOHNSEN A TTORNE KS Oct. 19, 1965 H. c. JOHNSENSEISMIC EXPLORATION 4 Sheets-Sheet 2 Filed Nov. 8, 1961 mtw M OZ wJOIPOIm mtmmdz M401 .rOIm

Y dfi-iEIS GNODEIS INVENTOR. H.C. JOHNSEN ATTORNEYS Oct. 19, 1965 H. c.JOHNSEN 3,212,599

SEISMIC EXPLORATION Filed Nov. 8, 1961 4 Sheets-Sheet a LEADS TO LEADSTO AMPLIFIER SHOT POSITIONS VSEISMOMETERS "1 Fla. 5

INVENTOR. FIG. 4 H.C. JOHNSEN 34 36! BY M A TTORNEVS Oct. 19, 1965 H. c.JOHNSEN SEISMIC EXPLORATION 4 Sheets-Sheet 4 Filed Nov. 8, 1961 INVENTORH. C. JOHNSEN BY 5 V E N R 0 T T A United States Patent 3,212,599SEISMIC EXPLORATION Harry (I. Johnsen, Bartlesville, 0kla., assignor toPhillips Petroleum Company, a corporation of Delaware Filed Nov. 8,1961, Ser. No. 150,909 2 Claims. (Cl. 181.5)

This invention relates to seismic exploration of subsurface geologicalformations, and more particularly to an improved method and apparatusfor carrying out such exploration. In another aspect, it relates to animproved method and apparatus for arranging, coupling, and operatingseismometer stations in an expeditious manner to reduce the expense,time and labor of reflection seismic operations in the field.

The art of carrying out seismic exploration of subsurface geologicalformations entails first of all the artificial production of elasticwaves at a first point near the earths surface and the detection of theresulting seismic waves at a series of second points at the earthssurface spaced from said first point. The elastic waves are commonlygenerated by detonating explosives in one or more shallow bore holes(each called the shotpoint or shothole). The elastic waves propagatedownwardly and outwardly into the subsurface formations and arerefracted and reflected by various discontinuities in the earthsstructure to the plurality of second points where the waves are detectedby a plurality of seismometer stations disposed in a predeterminedgeometric array in horizontally spaced relationship with the shotpoint.The seismometer stations convert the detected, reflected or refractedseismic waves into corresponding electrical seismic signals which areamplified and recorded. In seismic exploration today, it is thereflection seismic signal which is most commonly used in the study ofgeological formations, and it is reflection seismic exploration which isthe chief concern of this invention. The recorded reflection seismicsignals, in the form of a seismograph record or seismogram, are examinedand interpreted to locate and determine the nature of the geologicalstructures existing beneath the earths surface, such as the depth anddip of the subterranean reflecting beds.

A reflection seismic exploration technique which enjoys widespreadapplication is the method of continuous profiling, and the subjectinvention provides an improvement in this technique. In this technique,the seismometer stations are spaced uniformly along a prospect line. Aplurality of evenly spaced shotpoints are placed along the prospectline, or offset a constant distance therefrom, and intercept a constantnumber of seismometer stations. By generating elastic waves successivelyat each of the shotpoints, while advancing in one direction along theprospect line, a continuous profile or recording is obtained fromsuccessive continuous portions of the subsurface strata. In continuousprofiling, use is made of long seismometer cable spreads, therebyachieving the separation of multiple reverberations from primaryreflection signals. In shooting such a continuous seismic profile, ithas been the usual practice heretofore to move or advance the truckcarrying the amplifyingrecording equipment after each shot to thevicinity of the next shotpoint, and to physically pick up and move oradvance the seismometer cable and accompanying seismometer stations andset up the same at the new shotpoint. Since successive shotpoints may beon the order of several thousands of feet apart, it is evident thatconsiderable expense, time, and labor is expended by the seismic fieldparty in each day's work, if, as is customary, to setups are used eachday. The high cost of field operations makes the time factor ofparamount importance and those concerned with seismic opice eration areconstantly looking for Ways to reduce the expense, time, and effortexpended by the seismic field party.

Accordingly, an object of this invention is to improve seismicexploration of subsurface geological formations. Another object is toprovide an improved method and apparatus for arranging, coupling, andoperating seismometer stations in an expeditious manner to reduce theexpense, time, and labor of reflection seismic operations in the field;Another object is to provide an improved method and apparatus forincreasing the number of shotpoints which can be detonated and recordedduring one seismic setup. Another object is to provide an improvedmethod and apparatus for making continuous profiles of subsurfacegeological formations. Another object is to make use of long seismometercable spreads (e.g., 2 miles) in a more economical and convenientmanner. Further objects and advantages of this invention will becomeapparent to those skilled in the art from the following discussion,appended claims, and accompanying drawing in which:

FIGURE 1 is a view illustrating a typical common section cable used inthis invention;

FIGURE 2 is a diagram of a typical seismometer station used in thisinvention;

FIGURE 3 is a diagram illustrating the layout of seismometer cable intwo setups, according to this invention;

FIGURE 4 is a view illustrating the panel of a multishot switching unitused in this invention; and

FIGURE 5 is a diagram illustrating in detail a portion of the switchingunit of FIGURE 4;

FIGURE 6 is a diagram illustrating in detail a trip amplifier circuitused in this invention.

Referring now to the drawing, and initially to FIGURE 1, a typicalcommon section cable used in this invention is illustrated. This commonsection cable comprises a plurality of insulated pairs of conductorscovered by an extruded insulating sheet, one such pair of conductorsbeing provided for each seismometer station and adapted to conveyseismic signals. The common section cable is also provided with oneadditional pair of conductors which is used in common by all of theseismometer stations for the purpose which will be described in detailhereinafter. These conductors are connected at one end of the cable to amale plug or connector 1 and at the other end of the cable to a femaleplug or connector 2. Such mating plugs provide a means for couplingtogether in a predetermined fashion a plurality of such common sectioncables, so as to form a composite seismometer cable having conductorsrunning the length thereof. At fixed intervals along the length of thecommon section cable, there are provided a plurality of pairs ofconductor connectors 3a, 3b (each pair hereinafter referred to as atakeout, only one of which is shown in FIGURE 1). One connector of eachtakeout is permanently spliced to one conductor of a pair of conductorsand the other connector of the pair is permanently spliced to the otherconductor of such pair of conductors. One takeout thus made is providedfor each seismometer station. For example, a typical common sectioncable will have two or three such takeouts. In addition, the commonsection cable is provided with one or more additional takeouts or pairsof conductor connectors 4a, 4b, one such additional takeout beingprovided for each seismometer station, only one of which is shown inFIGURE 1. One connector of each of these additional takeouts ispermanently spliced to one conductor of a common pair of conductors inthe common section cable, and the other connector is permanently splicedto the other conductor of such pair of conductors. As will be apparenthereinafter, each takeout 4a, 4b is adapted to be connected to providecurrent to operate a relay lorepresented by one recording-trace.

cated at each seismometer station. When current is applied to this relayit connects one or more refraction seismometers at each station toconductor takeouts 3a, 3b. When the current is removed, the relay pointsprovide a connection to the plurality of reflection seismometers used todetect reflection seismic signals. Said additional takeouts 4a, 4b canalso be used alternately to connect a telephone to said common pair ofconductors in said common section cable, to provide communicationbetween the recording instrument operator and personnel using thetelephone. The common section cable can be provided with marks ofidentifying coloring or the like adjacent each connector so that theymay be readily distinguished and properly connected.

A typical common section cable may have a length of 960 feet and beprovided with three takeouts 3a, 3b, one such takeout being located inthe middle of the common section cable (480 feet from one end), one suchtakeout being located 165 feet from one end of the cable, and the othersuch takeout being located 165 feet from the other end of the cable.This typical common section cable can be provided with three additionaltakeouts 4a,.4b, one such takeout located 164 feet from one end, theother such takeout located 166 feet from the other end of the commonsection cable, and one such takeout located near the middle of saidcable (481 feet from one end).

Where the common section cable is to be used at other times inconjunction with locating the seismometer stations further apart (e.g.,450 feet instead of 300 feet), the common section cable can be providedwith additional takeouts 3a, 3b and additional takeouts 4a, 4b, thesetakeouts being taped to insulate them from the ground when not in use.In the typical common section cable described in the precedingparagraph, the common section cable can be provided with two such tapedtakeouts 3a, 3b, each located 240- feet from a different end of thecable, and two additional taped takeouts 4a, 412, one located 239 feetfrom one end and the other located 241 feet from the other end of thecommon section cable. Thus, a multi-purpose common section cable isprovided, with a varying number of takeouts, some of which are tapedwhen not in use.

FIGURE 2 illustrates a typical seismometer station and it comprises oneor more reflection seismometers 6,

tions thereof; this practice is called multiple detection,

the group of reflection seismometers 6 feeding a single channel of theamplifying-recording equipment and is The station further comprises oneor more refraction seismometers 7 disposed in substantially the middleof the array of reflection seismometers 6. The array of reflectionseismometers 6 are connected to the rest of the seismometer stationcircuitry by means of suitable mating connectors 9, 11. The seismometerstation is provided with first pair of takeout clips 12a, 12b, adaptedto be connected to one of the takeouts 3a, 3b of the common sectioncable, and thereby be placed in electrical circuit with one pair of theseismic 'signal conductors in the common section cable. The

other pair of clips 13a, 13b are adapted to be connected to one of thetakeouts 4a, 4b of the common section cable, and thereby be connected inelectrical circuit with said common pair of conductors in the commonsection cable. Solenoid 14 of relay switch 8 is connected by suitableconductors to clips 13a, 13b. One pole 16 of relay switch 8 is connectedby means of a conductor tomating connector 9 of the reflectionseismometer array, and one pole 17 is connected to refractionseismometer 7. The latter is in turn connected to clip 12b by aconductor, and the other mating connector 11 is connected to this latterconductor. Clip 12a is connected by a conductor to the contactor 18 ofrelay switch 8.

Referring now to the diagram of FIGURE 3 there is illustrated twoseismometer cable setups used in making continuous seismic profileaccording to this invention. This diagram illustrates how seismometercable is arranged and used for recording reflected seismic wavesproduced by successively generating shots at a plurality of shotpointsin a first setup, and how the seismometer cable can be incrementallyadvanced along a prospect line to record reflected seismic wavesproduced by successively generating shots at a plurality of shotpointsin a subsequent or second setup. First of all, a prospect line alongwhich it is desired to determine a continuous profile is determined, andthen a series of seismic shotholes are drilled, horizontally spacedapart along this line, to provide a plurality of shotpoints. A pluralityof seismometer stations, such as that illustrated in FIGURE 2, arehorizontally spaced apart along the prospect line where the shotholeshave been drilled. These seismometer stations are clipped to theappropriate takeouts of adjacent common section cables, such as shown inFIGURE 1. A plu rality of such common section cables are coupledtogether and strung out along the prospect line. A first plurality ofsuch coupled common section cables extend from one side of theshotpoint, and a second plurality of such coupled common section cablesextend in an opposite direction on one side of said shotpoint. One suchgroup of coupled common section cables comprise one seismometer cable28, and the other such group of coupled common section cables compriseanother seismometer cable 29.

These two seismometer cables extended in this manner comprise aseismometer setup. Adjacent ends of the two seismometer cables 28, 29are connected by means of mating connectors 31, 32 to a recording truck33 carrying amplifying-recording equipment, so that each pair of seismicsignal conductors may be connected to a corresponding amplifyingrecording circuit. The recording truck 33 is initially placed near thecenter of a first group of shotpoints. In recording the reflectedseismic events occasioned by successively generated shots in the firstgroup of shotpoints in the first setup, the recording truck remainsstationary, and only a common number (e.g., twenty-four) of seismometerstations are in electrical circuit with the amplifying-recordingequipment for each shot, such common number of stations thus connectedcalled a spread. In making each shot, the seismometer station adjacentsaid shotpoint is not connected to the amplifying-recording equipment.After each shot at one of the shotpoints, a different set of commonseismometer stations are connected to the amplifying-recording circuitby means of a gang switch or the like carried in the recording truck. Asthe shots are advanced along the prospect line, one or more of thetrailing seismometer stations in the setup are switched out of theamplifying-recording circuit, and one or more of the leading seismometerstations in the setup are switched in the amplifying-recording circuitby the gang switch.

After recording the reflected seismic signals produced by shots made ata plurality of shotpoints in the first setup, the recording truck isadvanced along the prospect line to a point near the center of a secondgroup of shotpoints, and for the purpose of recording the reflectionseismic signals produced by shots made at these new shotpoints, some ofthe trailing common section cables and accompanying seismometer stationsof the first setup can be disconnected and physically transported by acable truck in advance to the leading end of the first setup where theycan be connected to what was the leading common section cable of thefirst setup. Thereafter, seismic disturbances are generated at the newgroup of shotpoints in the second setup and the resulting seismicsignals recorded in the same manner as that employed in recording theseismic signals produced by seismic disturbances generated at the firstgroup of shotpoints in the first setup.

For example, in the first setup, a first group of seismometerv stations13-24 are disposed along the prospect line leading to the left ofShotpoint No. l, and a second group of seismometer stations 112 aredisposed along the prospect line leading to the right of ShotpointNo. 1. One seismometer cable 28, comprising common section cables a-e,and connected to seismometer stations I124, is connected by matingconnector 31 to the recording truck, and the other seismometer cable 29,comprising common section cables ,f to which are connected seismometerstations 1-10 and certain other seismometer stations not needed forShotpoint No. 1, is connected by means of mating connector 32 to therecording truck. Seismometer stations 1-24 are connected in separateamplifying-recording circuits and are used to record the seismicdisturbances generated at Shotpoint No. 1.

In preparing for the next shot at Shotpoint No. 2, certain of theseismometer stations are switched into the amplifying-recording circuit,and certain others are switched out of this circuit. For example, thetwo trailing seismometer stations of common section cable a are switchedout of this circuit, and the leading two seismometer stations of commonsection cable i are switched into the circuit. Further, the seismometerstation adjacent Shotpoint No. 2 is switched out of theamplifyingrecording circuit. A shot is fired at Shotpoint No. 2 and theseismic signals recorded in the same manner as before.

In preparing for the recording of the seismic signals occassioned by aseismic disturbance at Shotpoint No. 3, again certain of the trailingseismometer stations are switched out of the amplifying-recordingcircuit and certain of the leading seismometer stations are switchedinto this circuit by the gang switch. For example, all of theseismometer stations of common section cable a and the trailingseismometer station of common section cable b are switched out of theamplifying-recording circuit, and all but the first or leadingseismometer station of common section cable 1' are switched into thecircuit. The seismometer station adjacent Shotpoint No. 3 isdisconnected from common section cable f. A shot is then fired atShotpoint No. 3, and the seismic signals recorded as before.

For purposes of brevity, I have shown in FIGURE 3 and discussedhereinbefore the generation of seismic disturbances at only threeshotpoints, these shotpoints being located adjacent alternateseismometer stations. It is within the scope of this invention togenerate seismic disturbances adjacent successive seismometer stations,rather than skipping every other one as was done in FIG- URE 3, and toswitch into the amplifying-recording circuits a common number ofseismometer stations adjacent each of these shotpoints. For example,after the first shot at Shotpoint No. l and the recording of theresulting seismic signals, I can repeat the shot at the next adjacentseismometer station, the location of which will be adjacent the middleseismometer station connected to common section cable e. In this case,the trailing seismometer station connected to common section cable awill be switched out of the amplifying-recording circuit, and only thefirst two trailing seismometer stations connected to common sectioncable 1' will be switched into the circuit. Further, the middleseismometer station connected to common section cable i will be switchedinto the circuit. Further, the middle seismometer station connected tocommon section cable e will be switched out of the circuit, since such ashot is to be generated adjacent the location of this seismometerstation. It is thus seen that by using seismometer cables eachcomprising five coupled common section cables, each of which isconnected to three seismometer stations, I can make up to six shots inone setup, i.e., without moving the record truck while making the shotsand recording the resulting seismic signals.

When all of the seismometer stations of a trailing common section cableare switched out of the amplifyingrecording circuit, such common sectioncables and accompanying seismometer stations may be transported by acable truck to the leading end of the seismometer setup. Thesetransported cables are coupled to the leading common section cable forsubsequent shooting at the next setup. For example, in FIGURE 3, afterthe second shot is fired and the resulting seismic signals recorded,common section cable a and its accompanying seismometer stations may bedisconnected from the trailing end of common section cable b andtransported by the cable truck to the leading end of the seismometersetup where it may be laid out adjacent to the leading end ofseismometer cable preparatory to shooting at the subsequent setup. Or,after completing the shooting and recording at Shotpoint No. 3, commonsection cables a and b can be removed from the trailing end of theseismometer setup and transported to the leading end of the seismometersetup and connected thereto when shooting at the subsequent setup.

After thus moving the recording truck to the next group of shotpoints in.the second setup, and providing the requisite number of common sectioncables adjacent the leading end of the second setup, as described in thepreceding paragraph, the seismometer setup is ready to record theseismic signals produced by seismic disturbances successively made atthe new set of shotpoints. The making of these shots and the recordingof the resulting seismic signals in this second setup is carried out inthe same manner as first setup. The trailing common section cables usedin the second setup may be transported to the subsequent setup.

Rather than transporting the trailing common section cable to theleading end of the next setup right after it has served its purpose, allsuch used common section cables can be picked up and transported by thecable truck at the end of the day, and a suflicient number of additionalcommon section cables laid out in advance along the prospect 'lineduring the day, such additional cables being connected to the leadingend of the setups when necessary.

FIGURE 4 illustrates the panel of a multi-shot unit used in thisinvention. This unit is carried by the recording truck along with theamplifying-recording equipment. The unit is provided with two inputplugs 34, 35, one for each seismometer cable 28, 29 of FIGURE 3, and twooutplugs 36, 37 which are used to transmit the input seismic signals tocorresponding amplifiers. Within the unit there is provided one or moreswitches adapted to permit connecting the appropriate seismometerstations to corresponding amplifying-recording circuits. I prefer to usetwo switches, each provided with a plurality of stators or decks, suchas a 201887-G made by the Shallcross Mfg. Company, Collingdale, Penn..,as described in its Bulletin ALS 10M 1057, copyright 1957. Such switchesare ordinarily referred to in the art as gang switches, and theirconstruction and operation are well known to those skilled in the art.They comprise a plurality of stators or discs maintained on a shaft, theend of which is provided with a knob and a dial containing appropriatereference numbers. Such knobs are designated 38, 39 and such dialsdesignated 41, 42 in FIG- URE 4. In this application of such switches,the reference numbers 1, 2, 3 refer to the shotpoints of FIGURE 3. Oneof these switches in FIGURE 4 is associated with the leading seismometercable 28, and the other switch is associated with the trailingseismometer cable 29. In making a shot at Shotpoint No. 1 in FIG- URE 3,each of these two switches will be turned to No. 1 on the switch dial,after which these switches will be turned to No. 2 on the dial for thesecond shot, etc. Where six shots are made per setup in FIGURE 3,without skipping seismometer stations, such dials can be provided withreference numbers 1, 2, 3, 4, 5 and 6, one such number corresponding toeach of said six shots in said setup. Alternatively, the dials can beprovided with a scale for a six shotpoint setup and a scale for a fourshotpoint setup, thus allowing the same knob to be used for either typeof recording without rewiring the multishot unit. For example, the knobof the switch connected to stations 13-24 in a six shotpoint setup canbe turned to shotpoint number 8, and the input wiring for this shotpointwill be the same as shotpoint number 2 in a four shotpoint setup.

FIGURE diagrammatically illustrates a portion of such a gang switch. InFIGURE 5, the pairs of conductors connected to terminals on insulatedbar 46 are con- :nected to the corresponding conductors in the seis-:mometer cable. The other conductors connected to in- :sulated bar 47 onthe left hand side of FIGURE 5 are connected to correspondingamplifiers. The switch is provided with pairs of contactors 48a, 48b,and 49a, 4911, etc. Such contactors correspond to the rotors of the.gang switch, and move in unison. As schematically shown in FIGURE 5,such contactors move in unison to the right. In the position shown inFIGURE 5, which corresponds to Shot Position 1, contactors 48a, 48bconnect the pair of conductors 11, 12 from the seismometer cables toconductors 1, 2 leading to a corresponding amplifier No. 1. Similarly,in a position shown, contactors 49a, 49b connect the pair of conductors13, 14 from the seismometer cables to conductors 3, 4 of a correspondingamplifier No. 2, etc. In preparing for the second shot at Shotpoint No.2 of FIGURE 3, rotation of knobs 38, 39 to dial No. 2 in FIGURE 4results in the movement of the contactors of FIGURE 5 in unison to theright under Shot Position 2. With the contactors in this position shownby broken lines in FIGURE 5, contactors 48a, 48b, for example, will nowconnect conductors 7, 8 of the seismometer cables to conductors 1, 2 ofamplifier No. 1, etc. Similarly, when knobs 38, 39 of FIGURE 4 areswitched to No. 3 on the corresponding dials, the contactors of FIGURE 5will move to the right and occupy a position under Shot Position 3. Ofcourse, where more than three shots are fired per setup, and theswitches of FIGURE 4 are providedwith additional shotpoint numbers, andcontactors of FIGURE 5 are accordingly moved to other positionscorresponding to these other shotpoints.

In a typical operation of the apparatus shown in the drawing,preparation for firing a shot at Shotpoint No. 1 is made by switchingout the trailing seismometer station of common section cable e adjacentShotpoint No. 1. Switches 38 and 39 of FIGURE 4 are turned to dialposition No. 1, whereby the contactors of FIGURE 5 occupy the positionsunder Shot Position 1. An appropriate switch on the trip amplifiercircuit as shown in FIGURE 6 (such as that disclosed in US. 2,982,919issued May 2, 1961 to O. C. Montgomery) in the recording truck is thrownto send a current, e.g., 45 volts, along one pair of conductors 51a and51b in each of the seismometer cables, such current being transmitted toall seismometer stations of the seismometer setup. In each case, asshown in FIG- URE 2, this current is supplied to the solenoid 14 of therelay 8, causing contactor 18 to contact pole 17. As such, therefraction seismometer 7 is placed in electrical circuit with theseismic signal pair 3a, 3b of conductors in each common section cable.The initial seismic signals (called refraction signals) to reach eachseismometer station of the seismometer setup are detected by therefraction seismometer at each of the seismometer stations, and thesesignals are transmitted to the amplifiying-recording equipment throughlines 55a and 551;. Such equipment is provided with a trip amplifier 53circuit for each bank of twelve seismic recording amplifiers. Onefunction of the trip amplifier is to automatically remove the currentsupplied to relay 8 (FIGURE 2) at all seismometer stations through acommon pair of conductors in the seismometer cables. The trip amplifiercircuit for seismic amplifiers 1-12 is operated by the refractionsignals received from seismometer station 1. The same circuit foramplifiers 13-24 is operated by refraction signals received fromseismometer station 24. Since IQIiQLIS and 24 are farthest from theshotpoint, they receive their signals last. Therefore, refractionsignals are recorded from all 24 stations before reflection signals arereceived. When the current for relay 8, at all seismometer stations, isremoved, refraction seismometer 7 is automatically disconnected and thearray of reflection seismometers 6 is automatically connected to eachamplifying-recording circuit. Thereafter, the seismic signals reflectedfrom subsurface strata are detected by the reflection seismometers 6along the entire seismometer setup. These detected seismic events aretransmitted by the seismometer cables to the amplifying-recordingequipment on the record truck. In preparing for the second shot,switches 38 and 39 of FIGURE 4 are turned to dial position No. 2corresponding to the second shotpoint position, this switchingautomatically removing the two trailing seismometer stations of commonsection cable a from the amplifying-recording circuit, and automaticallyplacing the two leading seismometer stations of common section cable iin the circuit. At the same time, the seismometer station which wasadjacent Shotpoint No. 1 is switched in, this seismometer station nowcorresponding to station 14, and the seismometer station adjacent thesecond shotpoint, which was used as station 11 in recording the firstshot, is switched out. Next, the current from the 45-volt source isapplied to the relay switches of all seismometer stations in all cables.Again, this results in placing the refraction seismometers 7 of allstations 1 through 24 in the amplifying-recording circuit. A shot isthen fired at Shotpoint No. 2, and the initial seismic disturbancesdetected by the refraction seismometers 7 at all 24 seismometerstations. Thereafter, the reflection seismometers 6 at all 24 stationsof the seismometer setup are placed in the amplifyingrecording circuitand they detect the resulting seismic events.

The preparation for the third shot is accomplished in the same manner asbefore. As described hereinbefore, after the last shot is fired andrecorded in each setup, the recording truck is advanced to a point nearthe center of the next group of shotpoints, prior to which time therequisite number of seismometer stations have been placed adjacent tothe leading end of the subsequent setup.

This invention is particularly useful in carrying out the commonreflection point technique of continuous profiling disclosed and claimedin US. 2,732,906, issued January 31, 1956 to W. H. Mayne, but it is notnecessarily limited thereto. 9

Various modifications and alterations will become ap parent to thoseskilled in the art without departing from the scope and spirit of thisinvention, and it should be understood that the foregoing discussion andaccompanying drawing are not to be construed to limit unduly thisinvention.

I claim:

1. An improved system for conducting reflection seismic exploration,comprising in combination a plurality of common section seismometercables, said cables being positioned in a prospect line along a surfaceundergoing seismic exploration, wherein said plurality of cablesconstitute a set-up; a plurality of coupling means located at theextremities of each of said plurality of cables for coupling theextremities of adjacent cables together, said coupled cablesconstituting a seismometer spread with the total number of cables insuch a spread being constant and less than the number of cables in saidset-up, said spread extending the same distance on both sides of each ofa plurality of points along said prospect line; explosive means locatedat said plurality of points for generating seismic disturbances; arecording station for recording the reflection of said seismicdisturbances; an array of reflection seismometers located at each ofsaid plurality of points along said prospect line; at least onerefraction seismometer located at each of said plurality of points alongsaid prospect line, said refraction seismometer being in electricalcommunication with said recording station; a plurality of pairs ofconductors extending through said cables, said plurality having one pairfor connecting each array of reflection seismometers with said recordingstation; and one pair for connecting all the refraction seismometerswith said recording station; a plurality of relay means located at eachof said plurality of points; energizing means located in said recordingstation for energizing said relay means through said one pair ofconductors to place the refraction seismometers located at each of theplurality of points into electrical communication with said recordingstation at the time said seismic disturbances are first generated; atrip amplifier means operatively connected with that refractionseismometer located at the extremities of said seismometer spread, saidtrip amplifier being adapted to de-energize said relay means uponreceipt of a refraction signal from that refraction seismometer locatedat said extremity thereby placing the arrays of reflection seismometersinto electrical communication with said recording station; switchingmeans for simultaneously removing the seismometers located at one ormore trailing points from said seismometer spread and coupling to theleading ends thereof the seismometers located at one or more pointspositioned along said prospect line in advance of said seismometerspread.

2. An improved method for conducting reflection seismic exploration,said method comprising the steps of establishing a plurality of commonsection seismometer cables along a surface to be explored, saidplurality of cables constituting a set-up; coupling a plurality of saidcables together to form a seismometer spread wherein the total number ofcables in such a spread is constant and less than the number of saidcables in said set-up, said spread extending the same distance on bothsides of each of a plurality of points along a prospect line; locatingan array of reflection seismometers at each of said plurality of pointsalong said prospect line; locating at least one refraction seismometerat each of said plurality of points along said prospect line; generatingseismic disturbances at at least one of said plurality of points;initially detecting a plurality of refraction waves produced by saidseismic disturbances; recording said plurality of reflection waves;subsequently detecting the plurality of reflection waves produced bysaid seismic disturbances immediately upon recording of a refractionsignal from that refraction seismometer located at the extremity of saidseismometer spread; recording said plurality of reflection waves andswitching one or more trailing arrays of reflection seismometers fromsaid seismometer spread and switching into a leading end of saidseismometer spread one or more arrays of reflection seismometers in saidset-up positioned along said prospect line in advance of saidseismometer spread.

References Cited by the Examiner UNITED STATES PATENTS 2,088,588 7/37Dudley 181-.5 2,260,217 10/41 Eckhardt et al. 181-.5 2,317,334 4/43Shimek 181-05 2,321,450 6/43 Athy et al. l81-0.5 2,329,721 9/43 Hooveret al l81-O.5 3,105,568 10/63 Jolly 181.5

SAMUEL FEINBERG, Primary Examiner. CHESTER L. JUSTUS, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,3,212,599 October 19, 1965 Harry C. Johnsen It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 10, line 8, for "reflection" read refraction Signed and sealedthis 6th day of September 1966.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner ofPatents

2. AN IMPROVED METHOD FOR CONDUCTING REFLECTION SEISMIC EXPLORATION,SAID METHOD COMPRISING THE STEPS OF ESTABLISHING A PLURALITY OF COMMONSECTION SEISMOMETER CABLES ALONG A SURFACE TO BE EXPLORED, SAIDPLURALITY OF SID CABLES CONSITUTING A SET-UP; COUPLING A PLURALITY OFSAID CABLES TOGETHER TO FORM A SEISMOMETER SPREAD WHEREIN THE TOTALNUMBER OF CABLES IN SUCH A SPREAD IS CONSTANT AND LESS THAN THE NUMBEROF SAID CABLES IN SAID SET-UP, SAID SPREAD EXTENDING THE SAME DISTANCEON BOTH SIDES OF EACH OF PLURALITY OF POINTS ALONG A PROPSECT LINE;LOCATING IN ARRAY OF REFLECTION SEISMOMETERS AT EACH OF SAID PLURALITYOF POINTS ALONG SAID PROSPECT LINE; LOCATING AT LEAST ONE REFRACTIONSEISMOMETER AT EACH OF SAID PLURALITY OF POINTS ALONG SAID PROSPECTLINE; GENERATING SEISMIC DISTURBANCES AT LEAST ONE OF SAID PLURALITY OFPOINTS; INITIALLY DETECTING A PLURALITY OF REFRACTION WAVES PRODUCED BYSAID SEISMIC DISTURBACNES; RECORDING SAID PLURALITY OF REFLECTION